1. Field of the Invention
The present invention relates to an image-blur correcting viewing-optical system which corrects blur of an image by driving an image-blur correcting lens element in a direction perpendicular to the optical axis in accordance with the magnitude of a shake imposed on the image-blur correcting viewing-optical system.
2. Description of the Related Art
Two types of image-blur correcting viewing-optical systems have been known in the art:
(i) one which employs a variable angle prism; and
(ii) the other which employs an image-blur correcting lens element to be driven in a direction perpendicular to the optical axis.
In the case where a variable angle prism is employed (the above item (i)), since the boundary surfaces thereof exposed to air are flat, spherical aberration is inherently occurred, thereby chromatic aberration and decentering coma inevitably occur.
On the other hand, in the case where an image-blur correcting lens element is employed (the above item (ii)), since enough space for the image-blur correcting lens element to retreat has to be provided, and a space for a drive mechanism thereof is required accordingly, the size of the entire optical system has to be enlarged. The shape of the image-blur correcting lens element is, in particular, designed so that the shape of the exit pupil does not change even when the image-blur correcting lens element is decentered by the maximum amount in a direction perpendicular to the optical axis. Therefore the image-blur correcting lens element has to be made larger, still further, the thickness thereof also increases. Since the image-blur correcting lens element itself becomes heavier, a greater load is imposed on the drive mechanism thereof accordingly. As a result, a drive mechanism with strong driving force is required, which causes an increase in the size of the entire apparatus, and also causes an increase in production costs.
It is an object of the present invention to provide a small-sized image-blur correcting lens element, and further, provide a small-sized and light-weight image-blur correcting viewing-optical system in which the small-sized image-blur correcting lens element is employed.
In order to achieve the above-mentioned objects, there is provided an image-blur correcting viewing-optical system including an objective optical system, an image-erecting optical system and an eyepiece optical system. The objective optical system includes an image-blur correcting lens element which is driven in a direction perpendicular to the optical axis, and the image-blur correcting lens element satisfies the following condition:
1 mmxe2x89xa6xcfx86xe2x88x92xcfx860xe2x89xa63 mmxe2x80x83xe2x80x83(1)
wherein
xcfx86 designates a mechanical diameter of the image-blur correcting lens element; and
xcfx860 designates the diameter of an axial open aperture of the first surface of the image-blur correcting lens element.
The image-blur correcting viewing-optical system according to the present invention preferably satisfies the following condition:
0.04 less than DEC/xcfx86 less than 0.2xe2x80x83xe2x80x83(2)
wherein
DEC designates the maximum value for the correcting of decentering with respect to the image-blur correcting lens element (Decentering Amount).
In the case where the objective optical system is constituted by a front lens group and a rear lens group, either one of which is arranged to be the image-blur correcting lens element, the objective optical system can satisfy the following condition:
0.6 less than xcfx86c/xcfx86max less than 1.1xe2x80x83xe2x80x83(3)
wherein
xcfx86c designates the diameter of an axial open aperture of the object-side surface of the rear lens group of the objective optical system; and
xcfx86max designates the diameter of an axial open aperture of the object-side surface of the front lens group of the objective optical system.
The image-blur correcting lens element is preferably made from light-weight plastics for the purpose of load-reduction for the drive mechanism.
The present disclosure relates to subject matter contained in Japanese Patent Application No. Hei-11-226246 (filed on Aug. 10, 1999) which is expressly incorporated herein by reference in its entirety.